Speed responsive systems

ABSTRACT

This invention relates to a speed responsive system for a motor vehicle whereby the vehicle may be kept at a predetermined speed, or the driver may be warned when a predetermined speed is reached. In one embodiment, the system includes an inductive pick-up or transducer, which senses rotation of a ferrous-toothed disc rotatable with a shaft to generate a voltage dependent upon the rotational speed of the shaft. Means, comprising a potential divider or a memory circuit, are provided for generating a reference voltage, and a comparator circuit is provided for comparing the voltages, the comparator being arranged to emit or change its output signal when the speed responsive voltage, or a voltage derived therefrom, reaches the reference voltage.

[ SPEED nnsronsrvn SYSTEMS 1.

Inventors: John Noddings; Lawrence Edward Hyde; Roland Kenneth Burton,all of Leamington Spa, England [73] Assignee: Associated EngineeringLimited,

Leamington Spa, Warwickshire, England [22] Filed: Mar. 21, 1972 [21]Appl. No.: 236,658

[52] US. Cl. 317/5, 180/105 E [51] int. Cl B60k 31/00 [58] Field ofSearch 317/5; 180/105 E [56] References Cited UNITED STATES PATENTS3,575,256 4/1971 .lania 180/105 E 3,070,185 12/1962 Fales.... 180/105 E(let. 23, 1973 Primary ExaminerJ. D. Miller Assistant ExaminerHarry E.Moose, Jr. Attorney-Joseph F. Brisebois et a1,

[57] ABSTRACT This invention relates to a speed responsive system for amotor vehicle whereby the vehicle may be kept at a predetermined speed,or the driver may be warned when a predetermined speed is reached. Inone embodiment, the system includes an inductive pick-up or transducer,which senses rotation of a ferrous-toothed disc rotatable with a shaftto generate a voltage dependent upon the rotational speed of the shaft.Means, comprising a potential divider or a memory circuit, are providedfor generating a reference voltage, and a comparator circuit is providedfor comparing the voltages, the comparator being arranged to emit orchange its output signal when the speed responsive voltage, or a voltagederived therefrom, reaches the reference voltage.

3,546,533 12/1970 Lydick. 317/13 R 5 Claims 11 Drawing Figures 3,484,68612/1969 Wade 317 5 x 3,406,775 10/1968 Magnuski 317/5 x 8 REF Z9 com/424702 2/ THEOTI'LE 2g 7 .9 Nerd/Woe Q 13 5.5mm W 2 775557755 MFA/DRY)SYSTEM H (/ECU/T dv .224 31 QHWEE u/wr 0 d1 meal/E DECEEASE 25F 22 SY5TEM 2o F/FFEEE/VT/A TUE FREQUENC y 22 7 0- VDL 7A 55 flo/vvififwa/ PULSECDUNTEE V 4 71145 715/2 PATENTEU DU 2 3 I975 SHEET 1 [1F 7 PATENTEDUBI23 I915 SHEET U 0F 7 S E QM mix 52x ll UNm PATENTEUBCT 2 3 197a SHEET 5[IF 7 PATENTEU UB1 2 3 I873 SHEET 6 UF 7 mm a SHEET 7 [IF 7 PATENTEDUBI23 I975 m1 \uuuuuu N m) SPEED RESPONSIVE SYSTEMS This invention relatesto speed responsive systems and particularly, but not exclusively, tospeed responsive systems for motor vehicles whereby the vehicle may bekept at a predetermined speed, or the driver may be warned when apredetermined speed is reached.

According to the invention, a speed responsive systern includes meansfor generating an electrical voltage which changes with rotational speedof a rotatable member, means for generating a reference voltage, andcomparator means for comparing the voltages, the comparator beingarranged to emit or change its output signal when the speed responsivevoltage, or a voltage derived therefrom, reaches the reference voltage.Preferably the speed responsive system includes a feedback loop arrangedso that the output signal of the comparator, or a voltage controlledthereby is formed into pulses of which the average value increases withthe difference between the speed responsive voltage and the referencevoltage.

Conveniently the pulses are of substantially constant width and of afrequency which increases with the difference between the speedresponsive voltage and the reference voltage. Alternatively there isadded to the speed responsive voltage a voltage which changes with rateof change of the speed responsive voltage, the addition of the speedresponsive voltage and rate of change voltage being such that thecombined voltage will reach the reference voltage before the speedresponsive voltage alone reaches the reference voltage.

Conveniently the speed responsive voltage increases with increasingrotational speed of the member, and may be substantially proportional tothe rotational speed of the member.

Advantageously the rate of change voltage is substantially proportionalto the rate of change of the rotational speed of the member.

According to a feature of the invention, the rotatable member may bedriven by a prime mover having a control member for adjusting the outputtorque of the prime mover, and the output signal from the comparator isfed to means for adjusting the control member so as to regulate therotatable member to a substantially constant speed.

According to another feature, the rotatable member may be driven by aprime mover having a driver- -operable control member for adjusting theoutput torque of the prime mover, and the output signal from thecomparator indicates to the driver when the rotatable member reaches apredetermined speed. Preferably the comparator output signal is used togenerate a force tending to move the driver-operable control member in adirection which changes the rotatable speed towards a predeterminedspeed, against the action of the driver.

According to a further feature, the rotatable member may be driven by aprime mover having a driveroperable control member for adjusting theoutput torque of the prime mover, and the output signal from thecomparator is used to prevent the speed of the rotatable memberexceeding a predetermined speed, irrespective of any movement of thedriver-operable control member by the driver tending to increase therotatable member speed.

Suitably the reference voltage is produced by a potentiometer meansacross a supply voltage.

Alternatively the reference voltage is a voltage stored in an electricalmemory circuit by feeding into the memory circuit the speed responsivevoltage at an appropriate speed.

Conveniently the speed responsive voltage also feeds a voltmetercalibrated in terms of rotatable member speed.

In the case where the speed responsive voltage is produced fromelectrical pulses of which the frequency is proportional to therotatable member speed, the pulses may be fed to a pulse counter toindicate the number of rotatable member rotations.

Various embodiments of the invention are described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic layout of the speed responsive system,

FIG. 2 is a circuit diagram of part of FIG. 1,

FIG. 2a is an alternative circuit to FIG. 2,

FIG. 3 is a detail circuit diagram of part of FIG. 1, and

FIGS. 4 to 10 are diagrammatic sketches of parts of the speed responsivesystem controlled by the circuit diagram shown in FIG. 2.

In FIG. 1 a vehicle power unit 11 includes the usual engine and gear boxand drives an output shaft 12 to which is fastened a ferrous-tootheddisc or wheel 13. Adjacent the toothed wheel 13 is an inductivetransducer 14 of the kind which emits an electrical pulse as each toothon the wheel 13 passes. The pulse passes along a line 15 to afrequency-to-voltage converter 16 which emits an electrical voltageproportional to pulse frequency along a line 17. A pulse counter 18 isalso fed with the pulses and can be calibrated in terms of numbers ofrotations of the shaft 12 or, in a vehicle, in terms of distancetravelled. A voltmeter 19 is connected to the line 17 and is calibratedin terms of rotational speed of the shaft 12 or in terms of the vehiclespeed. A voltage V in line 17 is fed by a line 20 as one input to acomparator 21. The voltage V is also fed by a line 22 to adifferentiator 23 of which the outputvoltage is proportional to the rateof change of voltage V and is also fed by a line 24 as an input to thecompratator 21.

The voltage V is also fed through a set-memory switch 25 to anelectrical memory circuit 26. The latter sustains an output voltagewhich is equal to the value of the voltage V whenever the switch 25 ismomentarily closed. The memory circuit 26 output voltage is fed as athird input voltage V ref. into the comparator 21 through a switch 27.Alternatively V ref. can be derived from the slider 28 of apotentiometer 29 connected across the supply voltage and coupled to thecomparator 21 by the switch 27 in its other position.

When the comparator 21 emits an output signal it is fed to one of twotorque changing systems, namely either to a torque increase system 30 orto a torque decrease system 31. The torque increase and decrease systems30, 31 are arranged to operate a throttle actuator 32, movement of whichincreases or decreases appropriately the output torque of the power unit11.

In FIG. 2, transistors T, and T protected from reverse voltages bydiodes D and D amplify and limit the voltage picked up by the transducer14 due to the motion of the toothed wheel 13. The train of constantwidth constant amplitude pulses at the output of condenser C; feeds adiode/transistor pump circuit D T producing a voltage, at T collectorrelative to a stabilized voltage Vs, which is proportional to therotational speed of the toothed disc 13. This voltage may be set into amemory capacitor C4 by momentarily closing set-memory relay contacts RLAl which contacts correspond to those of the switch 25 in FIG. 1.

Field effect transistors T and T buffer the speedproportional andmemory'voltages producing V and V ref. which are fed to the comparator21. Since an F.E.T. has a very high input impedance, V ref. stays 7substantiallyconstant with time.

lf required, V ref. may be derived from the potentiometer 29 to give apreset speed, which may be adjusted by the driver to give control orgoverning of an attained vehicle speed, or it may be set and locked bythe'vehicle owner to give limitation of vehicle speed.

The voltage V is fed to the differentiator circuit 23 formed bytransistor T T-,, and associated components C R R R The output voltagedv/dt is proportional to the rate of change of V.

The voltages V ref., V and d'v/dt are fed to the comf parator circuit 21consisting of a differential amplifier formed by transistor T and T withconstant current drive from transistor T and associated components. Eachtorque changing system 30, 31 comprises a Schmitt trigger circuit anddriver, including transistors T T T for torque increase, and transistorsT T,,,, T for torque decrease.

Under normal driving conditions with the circuit on but not set tocontrol or govern the speed, the setmemory relay is energised to closecontacts RLA l, and V always equals V ref., and may vary with speed fromVs VGs down to about Vs/2 VGs (VGs being the equal gate source voltagesof the two matched F.E.T.s T and T Because of the comparator constantcurrent drive, the comparator circuit input'voltages, at the collectorsof transistors T and T are constant and equal. The input transistors areon so that the output and drive transistors T T are off and no drivecurrents are available from the output terminals D and U.

in a' control or governing mode the memory'relay contacts RL/\ 1 arevopened and V ref. is constant. If the speed of the shaft l2varies the'nV varies. If V goes greater than V ref. the torque-increase circuit-isoperated while the torque-decrease circuit is off. T vgoes off, T and Tcome on and current is available, from the output'terminal U for drivingthe throttle actuator 32.

If V goes less than V ref. the torque-decrease circuit is operated whilethe torque-increase circuit is held off. T goes off, T and T come on andcurrent is available, from the output terminal D, for driving thethrot-. tle actuator 32.

The differentiator feeds the comparator 21 with a voltage dv/dt,proportional to rate of change of output shaft speed. This has theeffect of stabilizing the system, by filling in the inevitable dead bandwhich exists between the torque increase and torque decrease controlmodes. The use of the bang-bang system with differential stabilizationmeansthat the throttle actuator design is simplified. [t is either on,in one or another direction, or inoperative in the dead band, therebyincreasing the system efficiency as regards supply currentconsumptioncompared with a proportional control system.

The action of the differentiator circuit 23 is as follows. When a drivesignal is initiated the throttle is moved to alter the shaft speed. Asthe speed alters, V alters, so a level dv/dt appears at the comparatorwhich adds or subtracts from V in an attempt to inhibit the drivesignal. The drive signal is therefore cancelled whilst the speed isstill in the trigger dead band. For a large error in V, for example whena vehicle suddenly encounters a steep hill, the drive current will pulseon and off rapidly until the dead band is reached, giving in effect aninching action to the throttle. The system is therefore stabilized bythe anticipatory action of the differentiating circuit.

FIG. 2a shows an alternative circuit to FIG. 2, which is in effect apulse operated proportional control system, although both circuits havemuch in common. The differentiator circuit is omitted in FIG. 2a and inits place there are incorporated two feedback loops, one from eachoutput terminal D and U. The feedback loop from terminal U comprises afeedback resistor R diode D and capacitor C connected, as shown, to theterminal U, the base' of transistor T and the 0 volts line. The feedbackloop from terminal D comprises feedback resistor R diode D and capacitorC connected to the terminal D, the base of transistor T and the 0 voltsline.

The action of the feedback loop from the terminal U is as follows, theaction of the loop from terminal D being identical. Normally the firsttransistor T of the relevant Schmitt trigger is on, and transistor T isoff, the driver transistor T being off also. Because of the diode Dthere is no feedback. As the input voltage to transistor T drops due toan error voltage from the comparator, the transistor T become switchedoff so that the transistor T comes on and its output voltage rises toV+, which is above the input voltage of transistor T Therefore, currentfeeds back through capacitor C which raises the input voltage oftransistor T to switch it on and thereby switch the driver transistor Toff. Capacitor C discharges through the resistances R',, and R until theoriginal voltage is reached, when the cycleis repeated. In this wayaseries of pulses appear at the terminal D, thepulses being ofsubstantially constant width (E6. 20 m8) determined by the time c orlstant of capacitor C and resistance R5, Each Schmitt trigger and outputdriver is effectivelya voltage operated pulse generator. Thepulsefrequency increases with the error signal until the relay or other drivecircuit operated by the terminal Dcannot respond to the frequency andstays on for large errors. If required the differentiator may beretained to give improved stability in difficult applications.

The system programming circuitry is shown in FIG. 3. By adding invarious switch functions the various modes of operating the'speedresponsive system may be realized.

S is a main selector switch having three positions and biased towardsthe third position by a spring 35. In the of position as shown, thecircuits are de-energised. In the on or centre position of S thecontacts S of switch S connected to the vehicle supply line voltage Vare closed, and as a result the control circuit is energized and thememory relay contacts RLA l of memory relay RLA are closed due tocurrent flowing via contacts RLB 1 of relay RLB and switch 8,, throughthe winding of memory relay RLA. The voltage on the memory capacitor Cis therefore always equal to the output voltage of thefrequency-to-voltage converter 16, provided that switch 27 is set to thememory position. When the switch S, is depressed to the third or biasedAUTO" position the relay RLB is energised via closed switch contacts Schanging over contacts RLB 1 which hold-in RLB when S is released to theON position. RLA is de-energised, so V ref. is now constant at a voltagedecided by that stored on the memory capacitor C The system is now inthe control or governing mode and the shaft speed will be maintainedsubstantially constant. A set of drop-out contacts S is arranged inseries with RLB so that if the vehicle brake or clutch pedal isdepressed the system drops out of AUTO and into the ON condition.

Advance of the controlled or governed speed may be obtained by holding Sin the AUTO position when RLA is held energized, via contacts S andtorque increase current is provided to the throttle actuator 32 viacontacts S The vehicle speed increases and V and V ref. increasetogether until S is released. Retard of the controlled or governed speedis obtained by switching to of than back to on when the throttle willclose. When the desired speed is reached, AUTO is reselected to resumecontrol. If a preset cruising speed is required, switch 27 is set to thereference position, when the speed is governed by the setting ofpotentiometer 29. The slider 28 may be calibrated in mph. and anydesired cruise speed may be set. Upon selecting AUTO the throttle willbe actuated to maintain the speed at that preset on potentiometer 29.The setting may be altered at will to advance or retard the speed byadjusting slider 28.

To return to a previously attained speed after initially reachingthespeed, switch S is opened thereby isolating RLA. When the system isdropped out RLB is arranged mechanically, or electrically via anotherpair of contacts, to inhibit actuator action. The reference voltageremains stored on the memory capacitor C,,. When AUTO" is again selectedthe vehicle speed will return to the previous value.

To remind the driver when the preset speed is reached or to limit thevehicles speed it is necessary to use a modified actuator. Basic controlcircuitry is the same as in FIGS. 2 and 3.

Various methods of actuation are shown in FIGS. 4 to 10. FIGS. 4 and 5show relaydriven control actuators.

In FIG. 4 air or mixture is fed to an engine (not shown) through anintake duct 40, having a normal throttle butterfly valve 41 rotatable bya spindle 42. In addition to the normal throttle linkage (not shown)connected to rotate the spindle 42, there is fixed at one end an arm 43connected by a chain 44 to a vacuum bellows actuator 45. A precompressedspring 46 normally extends the bellows 45 towards the closed throttleposition of the engine butterfly throttle valve 41.

The bellows 45 are connected by a duct 47 to an air control chamber 48.When the system is set to "AUTO relay RLB operates to move valve member49 to close an air bleed 50 into the air chamber 48.

When a torque increase voltage appears at terminal U solenoid RLU isenergised to raise a valve member 51 which admits manifold vacuum fromthe engine inlet manifold through a pipe 52 into the air chamber 48. Theensuing depression in the air chamber 48 causes the bellows 45 toretract and open the throttle valve 41. When the voltage on terminal Uis removed the valve member 51 again closes so that the throttle valve41 will be held at the obtaining position. If a torque decrease voltageappears at terminal D a solenoid RLD is energised which raises a valvemember 53 to admit air at atmospheric pressure through a pipe 54 intoair chamber 48. Thereupon the spring 46 causes the bellows 45 to expandand move the throttle valve 41 towards its closed position.

In FIG. 5 the arm 43 is rotated by a hydraulic slave cylinder and pistonassembly 55 which is connected by a pipe 56 to a hydraulic mastercylinder and piston assembly 57, of which the piston is moved by thethrottle pedal 58. In normal use therefore, the connection between thethrottle pedal 58 and the arm 43 is by a normal hydrostatic link.

An electric pump of the vibrating disphragm type commonly used as apetrol pump in vehicles is indicated generally at 59. The pump 59 has asolenoid 60 which, by its intermittant energization through contacts 61,causes a diaphragm piston 62 to be drawn back and forth. This movementdraws liquid from a reservoir 63 through an inlet non-return valve 64and forces it out through an outlet non-return valve 65 into the base ofa hydraulic cylinder 66. The pumped liquid circuit is completed by areturn pipe 67 which discharges into the reservoir 63, but is normallyclosed by a solenoidoperated ball valve 68. The pump 59 operates when atorque increase voltage appears at the terminal U. Since the return pipe67 is then closed, the pumped liquid entering the cylinder 66 causes thefree piston 69 therein to rise, displacing liquid from the member partof the cylinder 66 into the pipe 56, thereby opening the throttle valve41 irrespective of the movement of the throttle pedal 58. I

When the voltage at terminal U is removed and a torque decrease voltageappears at terminal D, a power transistor 70 conducts to pass energisingcurrent through the solenoid RLD which opens the ball valve 68 todischarge liquid from below the free piston 69 into the reservoir 63,thereby moving the throttle valve 41 towards its closed position. Inthis system the relay RLB is an ordinary relay with two sets ofcontacts. One set, RLB 1, holds the system ON; the other set, RLB 2,isolates the diaphragm pump in the OFF" and ON" positions, unless AUTOis selected.

FIGS. 6 and 7 show two types of dual purpose actua tor. These may beused for control and remind functions. In FIG. 6 the arm 43 is moved bya spring biased vacuum bellows actuator as in FIG. 4. In this case thelatter is connected to the arm 43 by a rod 71, having a sliding joint 72at its center. The sliding joint 72 is normally held rigid by apre-tensioned spring 73 to give direct connection between the bellows 45and arm 43. The control system in FIG. 6 is generally as in FIG. 4,except that an additional air chamber 74 is provided in the duct 47connected to the chamber 48 of FIG. 4. In the control mode air can passfreely along the duct 47 and through the further air chamber 74.

When the system in FIG. 6 is to operate in a mode where the driver willbe reminded when a predetermined speed is reached, a switch S is movedfrom a control position to a remind position. The switch S: in theremind position reverses the connections from the U and D terminals tothe respective sloenoids RLU and RLD, and also connects the power supplyto energise a solenoid valve RLC in the further air chamber 74. When thesolenoid RLC is energised its valve member 75 is moved to vent thebellows 45 to atmosphere through a valve 76, and to close them off fromthe air chamber 48 by a valve 77. A valve 78 is also opened to connectthe air chamber 48 through a duct 79 to further bellows 80, which arealso connected to the rod 71. If the vehicle speed is below the remindspeed a torque increase voltage appears at terminal U, which allows airto bleed into the further bellows 80 and give a normal feel to thethrottle pedal. If the vehicle speed is above the remind speed a reducedtorque voltage appears at terminal D, which applies vacuum to thefurther bellows 80. The latter try to move the rod 71 to the right inFIG. 6 and push the throttle pedal back against the drivers foot, givingthe pedal a hard feel.

If the driver wishes to exceed the remind speed, the extra force in therod 71 causes the sliding joint 72 to give. The driver is reminded ofhis excess speed by the extra pedal forces. A buzzer. or a lamp may beconnected to the terminal D to give additional warning.

In FIG. 7 the arm 43 is pulled to the left by a link 81 to open thethrottle. The end of the link 81 remote from the arm 43 is pivoted to arod 82 connected to the throttle pedal, and is also connected to one arm83 of a bell crank lever, of which the other arm 84 is made offerro-magnetic material such as mild steel. The bell crank lever ismounted on a common pivot with an actuator paddle 85 and with a furtherarm 86. The actuator paddle 85 and further arm 86 are connected by atension spring 87. The actuator paddle 85 carries an electro-magnet 88which when energised attracts and can clamp the actuator paddle 85 tothe bellcrank lever arm 84.

The further arm 86 is connected by a link 89 to a nut 90 which travelsalong a screw 91 when the latter is rotated. The screw 91 is driventhrough an appropriate gearing 92 by a split field electric motor 93,having field windings 94, 95. The field windings 94, 95 are controlledby the U and D terminals through power transistors 96, 97 respectively.I

When the nut 90 reaches the right hand end of the screw 91 it operates alimit switch 98 in series with the motor field winding 94 to preventfurther operation of the motor in that direction. I

When the system'is inoperative the nut 90 is driven to its right hand(i.e. full throttle) position, so that the actuator paddle 85 is out ofthe way of the bell crank lever arm 84. The driver can therefore use thethrottle pedal in the normal manner. In the control mode when the systemis set to AUTO" and the required speed is reached, the electromagnet 88is energised in parallel with relay RLB. The throttle pedal is depresseduntil the paddle 84 reaches the actuator paddle 85, when theelectro-magnet 88 clamps them together. If the speed of the vehicleincreases, the actuator paddle 85 is driven back towards the closedthrottle position by the electric motor 93 being fed with current at theD terminal until the correct throttle position for the required speed isattained. Since the limit switch 98 is now closed, current is fed to theD or U terminals as appropriate to maintain constant road speed. Thedriver may exceed the control speed by extra throttle pedal pressure,which will extend the spring 87. He may regain normal operation byswitching the control switch off or by pressing the brake pedal, so thatthe electro-magnet 88 becomes de-energised. The vehicle speed then dropsand actuator paddle 85 is driven to the full throttle position, therebyopening the limit swtich 98.

When the control switch is set to the speed remind position theelectro-magnet 88 cannot be energised. When the vehicle speed is belowthe remind speed the actuator paddle is at itsfull throttle position. Ifthe vehicle speed exceeds the remind speed the actuator paddle 85 isdriven down against the throttle paddle 84 and the driver feels extrapressure on his foot. The driver may drive with his foot lightly on thethrottle pedal so that he can just feel the extra pressure, and thevehicle speed will then be maintained at the selected value.

The remind speed may be exceeded for emergency purposes by extrapressure on the throttle pedal, caus' ing the spring 87 to extend.

FIGS. 8, 9 and 10 show types of speed limiting actuators. These allowthe driver to drive with the throttle pedal in the full-throttleposition while the control system adjusts the throttle 41 to maintain apreset speed. This type of system would be used, for example, oncommercial vehicles, hire cars or power boats, where the owner wished torestrict the maximum output shaft speed.

FIG. 8 shows an adaption of the system illustrated generally in FIG. 7.In FIG. 8 the throttle pedal 58 is connected by a link 100 to a paddle101. The link 81 connected to the throttle arm 43 is also connected topaddle 102, the paddles 101, 102 being freely pivoted on a' common shaft103. Overlapping portions of the paddles 101, 102 are arranged so thatas the throttle pedal 58 returns towards the closed throttle position,the paddle 101 forces the paddle 102 to close the throttle 41. However,contact between the paddles 101, 102 in the throttle opening directionis maintained only by a spring 104 for example a strong hairpin springsuitably arranged. The nut 90 is connected through its link 89 to afurther paddle 103, also freely pivoted on the shaft 103. Part of thepaddle 105 engages behind part of the paddle 102. In this way when thegoverned or controlled speed is exceeded, nut 90 will move towards theclosed throttle position driven by a motor actuator (not shown) so thatthe paddle 105 contacts the paddle 102 and forces it to rotate so as toclose the throttle 41. The spring 104 enables the paddle 101 to be leftbehind even if the throttle pedal is at its full throttle position.

This system shown in FIG. 8 is equally applicable to the system showngenerally in FIG. 4 if the bellows 45 are connected to the link 89 inplace of the nut 90.

FIG. 9 shows an adaption of a system shown generally in FIG. 5 toachieve a control or governing mode. In this case the feed line from thehydraulic pump 59 (not shown) and the return line 67 feed into thecylinder 66 above the piston 69. The piston 69 is urged to the top ofthe cylinder 66 by a spring 106. The piston 69 is connected by a rod 107to a smaller piston 108 in a corresponding cylinder 109. Upward movementof the pistons 69, 108 displaces liquid into the pipe 56 so as to openthe throttle. In this case the supply of current to the terminals D or Uwill cause appropriate quantities ofliquid to be pumped by the piston108 into or out of the pipe 56,.to provide corresponding opening orclosing of the throttle, irrespective of the position of the throttlepedal 58.

FIG. 10 shows a further modification of the system shown in FIG. 9, inwhich movement of the piston 108 is effected by the electricmotor-driven screw and nut system shown generally in FIG. 7.

We claim:

l. A speed responsive system, including means for generating anelectrical voltage which changes with rotational speed of a rotatablemember, means for generating a reference voltage, comparator means forcomparing the voltages, the comparator means being operable to producean output signal which changes when the speed responsive voltage reachesthe reference voltage, pulse generator circuit means including a timeconstant feedback loop, connected to the output of the comparator means,operable to form the output signal of the comparator means intosubstantially constant width pulses of which the average value increaseswith the difference between the speed responsive voltage and thereference voltage, and of which the frequency increases with thedifference between the speed responsive voltage and the referencevoltage.

2. A speed responsive system as claimed in claim 1, including adifferentiator circuit connected to the voltage generating means andadapted to produce an output voltage which changes with rate of changeof the speed responsive voltage, the output of the differentiatorcircuit being connected to the comparator means, the comparator meansbeing adapted to add the speed responsive voltage to the rate of changevoltage thereby to cause the combined voltage to reach the referencevoltage before the speed responsive voltage alone reaches the referencevoltage.

3. A speed responsive system as claimed in claim 4, wherein thedifferential circuit is adapted to produce a rate of change voltagesubstantially proportional to the rate of change of the rotational speedof the member.

4. A speed responsive system as claimed in claim I, wherein therotatable member is driven by a prime mover having a driver-operablecontrol member for adjusting the output torque of the prime mover, andthe output signal from the comparator is used to prevent the speed ofthe rotatable member exceeding a predetermined speed, irrespective ofany movement of the driver-operable control member by the driver tendingto increase the rotatable member speed.

5. A speed responsive system as claimed in claim 1, wherein the voltagegenerating means is connected to a voltmeter calibrated in terms ofrotatable member speed.

1. A speed responsive system, including means for generating an electrical voltage which changes with rotational speed of a rotatable member, means for generating a reference voltage, comparator means for comparing the voltages, the comparator means being operable to produce an output signal which changes when the speed responsive voltage reaches the reference voltage, pulse generator circuit means including a time constant feedback loop, connected to the output of the comparator means, operable to form the output signal of the comparator means into substantially constant width pulses of which the average value increases with the difference between the speed responsive voltage and the reference voltage, and of which the frequency increases with the difference between the speed responsive voltage and the reference voltage.
 2. A speed responsive system as claimed in claim 1, including a differentiator circuit connected to the voltage generating means and adapted to produce an output voltage which changes with rate of change of the speed responsive voltage, the output of the differentiator circuit being connected to the comparator means, the comparator means being adapted to add the speed responsive voltage to the rate of change voltage thereby to cause the combined voltage to reach the reference voltage before the speed responsive voltage alone reaches the reference voltage.
 3. A speed responsive system as claimed in claim 4, wherein the differential circuit is adapted to produce a rate of change voltage substantially proportional to the rate of change of the rotational speed of the member.
 4. A speed responsive system as claimed in claim 1, wherein the rotatable member is driven by a prime mover having a driver-operable control member for adjusting the output torque of the prime mover, and the output signal from the comparator is used to prevent the speed of the rotatable member exceeding a pRedetermined speed, irrespective of any movement of the driver-operable control member by the driver tending to increase the rotatable member speed.
 5. A speed responsive system as claimed in claim 1, wherein the voltage generating means is connected to a voltmeter calibrated in terms of rotatable member speed. 